Scaled Models Research Articles

An Ultrasonic Global Inspection Technique for an Offshore K-Joint

Abstract The catastrophic collapse of several offshore platforms has spurred the development of nondestructive inspection techniques for offshore structures. Presented here are the concepts of an ultrasonic global inspection technique. Also presented are the results of feasibility studies conducted on 119−, 110−, and ⅓-scale model K-joint models using this technique for early detection of damage. The technique takes advantage of the geometry of tubular joints to give global ultrasonic coverage of a joint while employing a similarity-coefficient-based algorithm for actual damage detection. The data from the scaled models indicate a correlation between the value of the similarity coefficient and the extent of induced damage. The results are encouraging for further development of the technique for field use.

Momentum and mass exchange during refill in scaled models of a PWR

Interfacial momentum and mass exchange between the liquid and gas phases in a PWR downcomer were investigated. A new momentum transfer correlation was developed from air-water experiments in 1 15 - and 2 15 - scale models of a PWR with standard and distorted geometries. The correlation is based on the Kutateladze parameter and indicates that the overall momentum transfer between the phases does not depend on scale for geometrically similar models. Interphase mass exchange has been included by evaluating the effective gas flow for momentum transfer. Predictions of the modified correlation agree quite well with experimental results of steam-water flows in three different scaled models of PWR's.

Nonlinear Wheelset Forces in Flange Contact—Part 2: Measurements Using Dynamically Scaled Models

This paper presents new experimental methods for the study of rail vehicle dynamics through the use of scaled models on tangent track, and the application of these techniques to the measurement of nonlinear wheelset force/displacement relations in steady-state. These relations are important to the analysis of wheelset response to track inputs, curving performance of trucks, and wheelclimb derailment. A one-fifth scale model instrumented wheelset with new wheel profiles is used, with similitude scaling of the contact forces achieved through use of a polycarbonate resin for the contact surfaces. Data are presented for wheelset lateral force and yaw moment for the nonlinear range of wheelset lateral displacements and yaw angles, including flange contact. The measured data validate the analytical model presented in Part 1 of this paper, based on nonlinear wheel/rail contact geometry, creep forces with adhesion limits, and wheelset kinematics. A criterion for wheelclimb derailment is presented and verified experimentally.

On structural‐acoustic scale modeling

Use of scale models to study the dynamic response of a fuselage structure subjected to acoustic excitation has many advantages. Recently, constructing a ring‐stiffened cylinder model of a fuselage for verifying some of the concepts for reducing cabin noise is being considered at Boeing. This has raised questions about the feasibility of using geometrically scaled models for simulating dynamic response of a pressurized fuselage structure. A review of the existing literature shows that it is possible to simulate the dynamic response using geometrically scaled models. The effect of internal pressurization was not considered earlier. It is observed that in order to preserve the scaling laws it is necessary to keep the same pressure differential in the model scale and the full scale structure. Another aspect that was not previously looked into in sufficient details was the effect of scaling down the fuselage stiffeners such as the stringers and frames on their natural frequencies. The importance of stiffener resonances on the low‐frequency vibration of the fuselage has been appreciated only recently [G. SenGupta, AIAA Paper 78‐504, 19th Structural Dynamics Conference (April 1978)]. It is shown that the relationship among the natural frequencies of the various components existing in a full scale structure can be easily preserved in the model scale structure. It is also shown that the structural‐acoustic scaling laws are considerably simplified if a structural Strouhal Number (SSN) is defined in terms of the speed of propagation of the bending waves (VB) in the structure. It is observed that the excitation convection speed in the model scale experiment should be the same as in the full scale, if coincidence excitation of the structure is to be properly simulated.

Acoustical Criteria for Auditoriums and Their Relation to Model Techniques

The first step in using model technique as a design tool is to establish a quantitative criterion (besides reverberation time). “Early to reverberant energy,” “steepness,” and “initial reverberation time” or “early decay time” (EDT) must be considered the most relevant factors, from aspects such as: (1) simplicity of measurement, (2) correlation with subjective assessments, and (3) possibility of comparing values obtained in scaled models with values obtained in full-size halls. Measured values of EDT may be applied either by calculating the inversion index, i.e., the average value in the audience area of a hall divided by the average value in the stage area, or by comparing values of EDT measured in different locations of a model (or a hall) with values of average reverberation time. These techniques have been applied in a number of 1:10 scale models and, also, in some completed halls.

Analyses and tests of thermal scale models of a simulated spacecraft.

This investigation of the feasibility of thermal scale modeling of spacecraft included analyses and tests of 0.285-, half-, and full-scale models of a simulated, double-walled cylindrical spacecraft. The design of the scaled models was based on the temperature preservation technique. Both steady-state and transient data were obtained from tests performed in the Boeing 10-ft-diam thermal-vacuum chamber equipped with a 4-ft solar simulator. The results have demonstrated the feasibility of using subscale models, designed according to the temperature preservation technique, to predict spacecraft temperatures under both steady-state and transient conditions. The majority of the model-predicted prototype temperatures agreed within 2% for the half-scale model and 3% for the 0.285-scale model. All significant deviations in the model-predicted prototype temperatures are accounted for through the accuracy of the thermal simulation, the model design, and the instrumentation. Had these deviations been eliminated, it is estimated that accuracies of 1% or less would have been realized.